L-NAC and L-NAC methyl ester prevent and overcome physical dependence to fentanyl in male rats.

N-acetyl-L-cysteine (L-NAC) is a proposed therapeutic for opioid use disorder. This study determined whether co-injections of L-NAC (500 µmol/kg, IV) or its highly cell-penetrant analogue, L-NAC methyl ester (L-NACme, 500 µmol/kg, IV), prevent acquisition of acute physical dependence induced by twice-daily injections of fentanyl (125 µg/kg, IV), and overcome acquired dependence to these injections in freely-moving male Sprague Dawley rats. The injection of the opioid receptor antagonist, naloxone HCl (NLX; 1.5 mg/kg, IV), elicited a series of withdrawal phenomena (i.e. behavioral and cardiorespiratory responses, hypothermia and body weight loss) in rats that received 5 or 10 injections of fentanyl and similar numbers of vehicle co-injections. With respect to the development of dependence, the NLX-precipitated withdrawal phenomena were reduced in rats that received had co-injections of L-NAC, and more greatly reduced in rats that received co-injections of L-NACme. In regard to overcoming established dependence, the NLX-precipitated withdrawal phenomena in rats that had received 10 injections of fentanyl (125 µg/kg, IV) were reduced in rats that had received co-injections of L-NAC, and more greatly reduced in rats that received co-injections of L-NACme beginning with injection 6 of fentanyl. This study provides compelling evidence that co-injections of L-NAC and L-NACme prevent the acquisition of physical dependence and overcome acquired dependence to fentanyl in male rats. The higher efficacy of L-NACme is likely due to its greater cell penetrability in brain regions mediating dependence to fentanyl and interaction with intracellular signaling cascades, including redox-dependent processes, responsible for the acquisition of physical dependence to fentanyl.

The arousal effect of An-Gong-Niu-Huang-Wan on alcoholic-induced coma rats: A research based on EEG.

ETHNOPHARMACOLOGICAL RELEVANCE: Acute alcohol intoxication is one of the leading causes of coma. A well-regarded Chinese herbal formula, known as An-Gong-Niu-Huang-Wan (AGNHW), has garnered recognition for its efficacy in treating various brain disorders associated with impaired consciousness, including acute alcohol-induced coma. Despite its clinical effectiveness, the scientific community lacks comprehensive research on the mechanistic aspects of AGNHW's impact on the electroencephalogram (EEG) patterns observed during alcohol-induced coma. Gaining a deeper understanding of AGNHW's mechanism of action in relation to EEG characteristics would hold immense importance, serving as a solid foundation for further advancing its clinical therapeutic application. AIM OF THE STUDY: The study sought to investigate the impact of AGNHW on EEG activity and sleep EEG patterns in rats with alcoholic-induced coma. MATERIALS AND METHODS: A rat model of alcohol-induced coma was used to examine the effects of AGNHW on EEG patterns. Male Sprague-Dawley rats were intraperitoneally injected with 32% ethanol to induce a coma, followed by treatment with AGNHW. Wireless electrodes were implanted in the cortex of the rats to obtain EEG signals. Our analysis focused on evaluating alterations in the Rat Coma Scale (RCS), as well as assessing changes in the frequency and distribution of EEG patterns, sleep rhythms, and body temperature subsequent to AGNHW treatment. RESULTS: The study found a significant increase in the δ-band power ratio, as well as a decrease in RCS scores and ß-band power ratio after modeling. AGNHW treatment significantly reduced the δ-band power ratio and increased the ß-band power ratio compared to naloxone, suggesting its superior arousal effects. The results also revealed a decrease in the time proportion of WAKE and REM EEG patterns after modeling, accompanied by a significant increase in the time proportion of NREM EEG patterns. Both naloxone and AGNHW effectively counteracted the disordered sleep EEG patterns. Additionally, AGNHW was more effective than naloxone in improving hypothermia caused by acute alcohol poisoning in rats. CONCLUSION: Our study provides evidence for the arousal effects of AGNHW in alcohol-induced coma rats. It also suggests a potential role for AGNHW in regulating post-comatose sleep rhythm disorders.

Unveiling the antinociceptive mechanisms of Methyl-2-(4-chloro-phenyl)-5-benzoxazoleacetate: insights from nociceptive assays in mice.

OBJECTIVE: Methyl-2-(4-chloro- phenyl)-5-benzoxazoleacetate (MCBA), a synthetic benzoxazole derivative with established antipsoriatic efficacy, was investigated for potential antinociceptive effects. This study employs various nociceptive assays in mice to elucidate MCBA's antinociceptive mechanisms. MATERIALS AND METHODS: MCBA's antinociceptive potential was tested against various nociception models induced by formalin, glutamate, capsaicin, a transient receptor potential vanilloid 1 (TRPV1) receptor agonist, and phorbol 12-myristate 13-acetate, a protein kinase C (PKC) activator. It was then assessed using the hot plate test and examined within the acetic acid-induced writhing test. During the acetic acid-induced writhing test, MCBA was pre-challenged against selective receptor antagonists such as naloxone, caffeine, atropine, yohimbine, ondansetron, and haloperidol. It was also pre-challenged with ATP-sensitive potassium channel inhibitor (glibenclamide) to further elucidate its antinociceptive mechanism. RESULTS: The results showed that oral administration of MCBA led to a dose-dependent and significant inhibition (p < 0.05) of nociceptive effects across all evaluated models at doses of 60, 120, and 240 mg/kg. Moreover, the efficacy of MCBA's antinociceptive potential was significantly counteracted (p < 0.0001) by specific antagonists: (i) directed at adenosinergic, alpha-2 adrenergic, and cholinergic receptors using caffeine, yohimbine, and atropine, respectively; and (ii) targeting ATP-sensitive potassium channels, employing glibenclamide. Antagonists aimed at opioidergic and serotoninergic receptors (naloxone and ondansetron, respectively) had poor utility in inhibiting antinociceptive activity. Conversely, the dopaminergic receptor antagonist haloperidol potentiated locomotor abnormalities associated with MCBA treatment. CONCLUSIONS: MCBA-induced antinociception involves modulation of glutamatergic-, TRVP1 receptors- and PKC-signaling pathways. It impacts adenosinergic, alpha-2 adrenergic, and cholinergic receptors and opens ATP-sensitive potassium channels.

The Role of Opioid Receptor Antagonists in Regulation of Blood Pressure and T-Cell Activation in Mice Selected for High Analgesia Induced by Swim Stress.

Opioid peptides and their G protein-coupled receptors are important regulators within the cardiovascular system, implicated in the modulation of both heart and vascular functions. It is known that naloxone-an opioid antagonist-may exert a hypertensive effect. Recent experimental and clinical evidence supports the important role of inflammatory mechanisms in hypertension. Since opioids may play a role in the regulation of both blood pressure and immune response, we studied these two processes in our model. We aimed to evaluate the effect of selective and non-selective opioid receptor antagonists on blood pressure and T-cell activation in a mouse model of high swim stress-induced analgesia. Blood pressure was measured before and during the infusion of opioid receptor antagonists using a non-invasive tail-cuff measurement system. To assess the activation of T-cells, flow cytometry was used. We discovered that the non-selective antagonism of the opioid system by naloxone caused a significant elevation of blood pressure. The selective antagonism of µ and κ but not δ opioid receptors significantly increased systolic blood pressure. Subsequently, a brief characterization of T-cell subsets was performed. We found that the blockade of µ and δ receptors is associated with the increased expression of CD69 on CD4 T-cells. Moreover, we observed an increase in the central memory CD4 and central memory CD8 T-cell populations after the δ opioid receptor blockade. The antagonism of the µ opioid receptor increased the CD8 effector and central memory T-cell populations.

Opioid receptor antagonists reduce motivated wheel-running behavior in mice.

We hypothesized that opioid receptor antagonists would inhibit motivated behavior produced by a natural reward. To evaluate motivated responses to a natural reward, mice were given access to running wheels for 71.5 h in a multi-configuration testing apparatus. In addition to a running wheel activity, locomotor activity (outside of the wheel), food and water intake, and access to a food container were measured in the apparatus. Mice were also tested separately for novel-object exploration to investigate whether naloxone affects behavior unrelated to natural reward. In untreated mice wheel running increased from day 1 to day 3. The selective µ-opioid receptor antagonist ß-funaltrexamine (ß-FNA) (5 mg/kg) slightly decreased wheel running, but did not affect the increase in wheel running from day 1 to day 3. The non-selective opioid receptor antagonist naloxone produced a greater reduction in wheel running than ß-FNA and eliminated the increase in wheel running that occurred over time in the other groups. Analysis of food access, locomotor behavior, and behavior in the novel-object test suggested that the reduction in wheel running was selective for this highly reinforcing behavior. These results indicate that opioid receptor antagonism reduces responses to the natural rewarding effects of wheel running and that these effects involve multiple opioid receptors since the non-selective opioid receptor antagonist had greater effects than the selective µ-opioid receptor antagonist. It is possible that at the doses employed, other receptor systems than opioid receptors might be involved, at least in part, in the effect of naloxone and ß-FNA.

Assessing effects of tamoxifen on tolerance, dependence, and glutamate and glutamine levels in frontal cortex and hippocampus in chronic morphine treatment.

Tamoxifen has been shown to reduce glutamate release from presynaptic glutamatergic nerves and reverse tolerance to morphine-induced respiratory depression. Changes in glutamatergic neurotransmission in the central nervous system contribute to morphine tolerance, dependence, and withdrawal. This study, therefore, evaluated effects of tamoxifen on development of analgesic tolerance and dependence, and brain glutamate and glutamine levels in chronic morphine administration. Mice implanted with placebo or morphine pellets were injected with tamoxifen (0.6-2 mg/kg) or vehicle twice daily for 3 days. Nociceptive response was evaluated in the hot plate and tail immersion tests, 4, 48 and 72 h post-implant, and following a challenge dose of morphine (10 mg/kg). Withdrawal signs were determined after naloxone (1 mg/kg) administration. Morphine increased nociceptive threshold which declined over time. At 72 h, acute morphine elicited tolerance to the analgesic effect in the hot plate test in vehicle or tamoxifen administered animals. In the tail immersion test, however, tolerance to morphine analgesia was observed in tamoxifen, but not vehicle, co-administration. Tamoxifen did not reduce withdrawal signs. In contrast to previous reports, glutamate and glutamine levels in the hippocampus and frontal cortex did not change in the morphine-vehicle group. Confirming previous findings, tamoxifen (2 mg/kg) decreased glutamate and glutamine concentrations in the hippocampus in animals with placebo pellets. Both doses of tamoxifen significantly changed glutamate and/or glutamine concentrations in both regions in morphine pellet implanted animals. These results suggest that tamoxifen has no effect on dependence but may facilitate tolerance development to the antinociception, possibly mediated at the spinal level, in chronic morphine administration.

µ-Opioid receptor antagonism facilitates the anxiolytic-like effect of oxytocin in mice.

Mood and anxiety disorders are leading causes of disability worldwide and are major contributors to the global burden of diseases. Neuropeptides, such as oxytocin and opioid peptides, are important for emotion regulation. Previous studies have demonstrated that oxytocin reduced depression- and anxiety-like behavior in male and female mice, and opioid receptor activation reduced depression-like behavior. However, it remains unclear whether the endogenous opioid system interacts with the oxytocin system to facilitate emotion regulation in male and female mice. We hypothesized that opioid receptor blockade would inhibit the anxiolytic- and antidepressant-like effects of oxytocin. In this study, we systemically administered naloxone, a preferential µ-opioid receptor antagonist, and then intracerebroventricularly administered oxytocin. We then tested mice on the elevated zero maze and the tail suspension tests, respective tests of anxiety- and depression-like behavior. Contrary to our initial hypothesis, naloxone potentiated the anxiolytic-like, but not the antidepressant-like, effect of oxytocin. Using a selective µ-opioid receptor antagonist, D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2, and a selective κ-opioid receptor antagonist, norbinaltorphimine, we demonstrate that µ-opioid receptor blockade potentiated the anxiolytic-like effect of oxytocin, whereas κ-opioid receptor blockade inhibited the oxytocin-induced anxiolytic-like effects. The present results suggest that endogenous opioids can regulate the oxytocin system to modulate anxiety-like behavior. Potential clinical implications of these findings are discussed.

Intracerebroventricular administration of TRH Agonist, RX-77368 alleviates visceral pain induced by colorectal distension in rats.

Thyrotropin-releasing hormone (TRH) acts centrally to exert pleiotropic actions independently from its endocrine function, including antinociceptive effects against somatic pain in rodents. Whether exogenous or endogenous activation of TRH signaling in the brain modulates visceral pain is unknown. Adult male Sprague-Dawley rats received an intracerebroventricular (ICV) injection of the stable TRH analog, RX-77368 (10, 30 and 100 ng/rat) or saline (5 µl) or were semi-restrained and exposed to cold (4°C) for 45 min. The visceromotor response (VMR) to graded phasic colorectal distensions (CRD) was monitored using non-invasive intracolonic pressure manometry. Naloxone (1 mg/kg) was injected subcutaneously 10 min before ICV RX-77368 or saline. Fecal pellet output was monitored for 1 h after ICV injection. RX-77368 ICV (10, 30 and 100 ng/rat) reduced significantly the VMR by 56.7%, 67.1% and 81.1% at 40 mmHg and by 30.3%, 58.9% and 87.4% at 60 mmHg respectively vs ICV saline. Naloxone reduced RX-77368 (30 and 100 ng, ICV) analgesic response by 51% and 28% at 40 mmHg and by 30% and 33% at 60 mmHg respectively, but had no effect per se. The visceral analgesia was mimicked by the acute exposure to cold. At the doses of 30 and 100 ng, ICV RX-77368 induced defecation within 30 min. These data established the antinociceptive action of RX-77368 injected ICV in a model of visceral pain induced by colonic distension through recruitment of both opioid and non-opioid dependent mechanisms.

Memantine and SKF82958 but not an enriched environment modulate naloxone-precipitated morphine abstinence syndrome without affecting hippocampal tPA mRNA levels in rats.

There is accumulating evidence supporting the involvement of tissue-plasminogen activator (tPA) in the mechanisms underlying the effects of morphine and an enriched environment. This study was designed to investigate possible interactive roles of the glutamatergic and the dopaminergic systems regarding hippocampal tPA in the neurobiology of morphine dependence. For this purpose, Wistar albino rats, housed in either a standard- (SE) or an enriched environment (EE) were implanted subcutaneously with morphine (150 mg base) or placebo pellets. Behavioral and somatic signs of morphine abstinence precipitated by an opioid-receptor antagonist naloxone (1 mg/kg, i.p.) 72 h after the pellet implantation were observed individually for 15 min in all groups. Memantine (10 mg/kg i.p.), an antagonist of N-methyl-D-aspartic acid class of glutamatergic receptor-subtype decreased teeth-chattering, ptosis, diarrhea and the loss of body weight. SKF82958 (1 mg/kg, i.p.), a dopamine D1-receptor agonist decreased jumping and ptosis but increased rearing and loss of body weight. On the other hand, co-administration of SKF82958 with memantine prevented some of their effects that occur when administered alone at the same doses. Furthermore, the EE did not change the intensity of morphine abstinence. The level of hippocampal tPA mRNA was found to be lower in the SE morphine abstinence group than in the placebo group and close to the EE morphine abstinence group, whereas there was no significant alteration of its level in the memantine or SKF82958 groups. These findings suggest that the interaction between the glutamatergic and the dopaminergic systems may be an important component of the neurobiology of morphine dependence, and the role of tPA in this interaction should be further investigated.

A novel investigation of placebo analgesia through social communication in mice.

BACKGROUND AND AIMS: In rodents, placebo analgesia is often investigated through direct conditioning of stimuli, but humans can experience placebo analgesia through expectation without experience. In this study, we sought to determine whether placebo analgesia could be elicited through social communication. METHODS: Male and female mice were housed in pairs (designated "Active" and "Bystander") and tested for thermal thresholds on a hot plate (53 °C). Food restriction (1 hr/day) was implemented. The Active mouse was taken to a new cage with food dusted with cocoa (COC) or cinnamon (CINN). The Bystander mice were given regular chow in the home cage. After feeding, the Active mice were given morphine (5 mg/kg, SC) or saline and tested on the hot plate. After 5 pairings of a flavor and treatment (counterbalanced), Active mice were tested following access to a flavored food. Bystander mice were given their first direct exposure to a flavored food and tested on the hot plate. The protocol was repeated with naloxone (10 mg/kg, IP) administered prior to testing. Finally, mice were tested in a two-choice test with both flavored foods available. RESULTS: Active mice showed a conditioned analgesic response to the morphine-paired flavor that was reduced by naloxone. Bystander mice showed a placebo analgesic response to their cagemate's morphine-paired flavor that was not significantly impacted by naloxone. Bystander mice spent more time in the chamber associated with their cagemate's morphine-paired flavor. CONCLUSIONS: To our knowledge, this is the first investigation of placebo analgesia without direct conditioning, instead relying on social communication between mice. The lack of effect with naloxone pretreatment suggests an opioid-independent effect in the Bystander mice. Placebo analgesia in mice may be possible without direct conditioning to better model the effect of expectation of a novel analgesic in humans.

Rats chasing the dragon: A new heroin inhalation method.

BACKGROUND: Despite extensive human use of inhalation for ingesting opioids, models in rodents have mostly been limited to parenteral injection and oral dosing. Methods using electronic drug delivery systems (EDDS; "e-cigarettes") have shown efficacy in rodent models but these do not faithfully mimic the most popular human inhalation method of heating heroin to the point of vaporization. NEW METHOD: Middle aged rats were exposed to vapor created by direct heating of heroin HCl powder in a ceramic e-cigarette type atomizer. Efficacy was determined with a warm water tail withdrawal nociception assay, rectal temperature and self-administration. RESULTS: Ten minutes of inhalation of vaporized heroin slowed response latency in a warm water tail withdrawal assay and increased rectal temperature in male rats, in a dose-dependent manner. Similar antinociceptive effects in female rats were attenuated by the opioid antagonist naloxone (1.0 mg/kg, s.c.). Female rats made operant responses for heroin vapor in 15-minute sessions, increased their response rate when the reinforcement ratio increased from FR1 to FR5, and further increased their responding when vapor delivery was omitted. Anti-nociceptive effects of self-administered volatilized heroin were of a similar magnitude as those produced by the 10-minute non-contingent exposure. COMPARISON WITH EXISTING METHODS: Inhalation of directly volatilized heroin successfully produces heroin-typical effects, comparable to EDDS inhalation delivery. CONCLUSIONS: This study shows that "chasing the dragon" methods of inhalation of heroin can be modeled successfully in the rat. Inhalation techniques may be particularly useful for longer term studies deep into the middle age of rats.

Evaluation of the anti-nociceptive profile of essential oil from Melissa officinalis L. (lemon balm) in acute and chronic pain models.

ETHNOPHARMACOLOGICAL RELEVANCE: Melissa officinalis L. (Lamiaceae) is a medicinal plant native to Mediterranean regions and found in other parts of the world. Extracts and essential oil from this widely cultivated culinary medicinal herb are used in traditional medicine to manage a variety of disorders that include epilepsy and pain. AIM OF THE STUDY: To assess the anti-nociceptive potentials of Melissa officinalis essential oil (MO) and probe the involvement of adrenergic, opioidergic, serotonergic and potassium adenosine triphosphate (KATP) mechanisms in its anti-nociceptive effects. MATERIAL AND METHODS: We employed formalin-, acetic acid and hot plate-induced nociception to study the acute anti-nociceptive effects of MO. The sciatic nerve injury (CCI) model of neuropathic pain was utilized to study the anti-nociceptive effects of MO on chronic pain. Effects of MO on anxiety, cognitive deficits, oxidative stress and inflammation in the CCI rats were evaluated on elevated plus maze, open field test, novel object recognition, oxidative stress parameters and pro-inflammatory cytokines, respectively. The possible mechanism(s) of MO's anti-nociceptive effects were elucidated using prazosin, yohimbine, propranolol, glibenclimide, naloxone and metergoline, which are acknowledged antagonists for α1-, α2- and ß-adrenergic, potassium adenosine triphosphate (KATP), opioidergic and serotonergic systems, respectively. RESULTS: MO significantly attenuated acetic acid- and formalin-induced nociception; prolonged the mean reaction time of rats on hot plate before and following sciatic nerve chronic injury (CCI). MO ameliorated anxiety, cognitive deficits and oxidative stress, reduced pro-inflammatory cytokine levels and produced a near total restoration of injured sciatic nerves in CCI rats. Naloxone, metergoline and glibenclimide significantly blocked, while prazosin, yohimbine and popranolol failed to block the anti-nociceptive effects of MO in formalin-induced nociception. CONCLUSIONS: MO contains biologically active compounds with potential anti-nociceptive properties that modulate KATP, opioidergic and serotonergic pathways. These support the development of bioactive compounds from MO as anti-nociceptive agents.

Buprenorphine-Naloxone Maintenance and Lactation.

BACKGROUND: Breastfeeding among lactating people with opioid use disorder taking buprenorphine monotherapy is generally accepted, as low concentrations of buprenorphine and metabolites in human milk have been well-established. The use of buprenorphine-naloxone for pregnant and lactating people with opioid use disorder is expanding and there is no information available regarding the concentrations of naloxone and their metabolites in human milk to recommend the use of this combination medication during lactation. RESEARCH AIMS: To determine the concentrations of buprenorphine and naloxone and their primary metabolites in human milk, maternal plasma, and infant plasma, among lactating buprenorphine-naloxone maintained people and their infants. METHODS: Four lactating buprenorphine-naloxone maintained people provided plasma and human milk samples on Days 2, 3, 4, 14, and 30 postpartum. Infant plasma was obtained on Day 14. RESULTS: Concentrations of buprenorphine, norbuprenorphine and their glucuronide metabolites were present in maternal plasma and human milk at low concentrations, consistent with previous research in lactating buprenorphine monotherapy participants. Naloxone was not detected, or was detected at concentrations below the limit of quantification, in maternal plasma and in all except one human milk sample at Day 30. Naloxone was not detected or detected at concentrations below the limit of quantification in all infant plasma samples. CONCLUSION: Results support the use of buprenorphine-naloxone by lactating people who meet appropriate criteria for breastfeeding.

Zingerone Alleviates Morphine Tolerance and Dependence in Mice by Reducing Oxidative Stress-Mediated NLRP3 Inflammasome Activation.

Morphine (MPH) is widely used for pain management; however, long-term MPH therapy results in antinociceptive tolerance and physical dependence, limiting its clinical use. Zingerone (ZIN) is a natural phenolic compound with neuroprotective effects. We investigated the effects of single and repeated doses of ZIN on MPH-induced tolerance, dependence, and underlying biochemical mechanisms. After a dose-response experiment, tolerance was developed to MPH (10 mg/kg, i.p.) for seven days. In the single-dose study, ZIN was administered on day seven. In the repeated-dose study, ZIN was administered for seven days. Naloxone (5 mg/kg, i.p., 120 min after MPH) was injected to assess withdrawal signs on day seven. The levels of thiobarbituric acid reactive substances (TBARS), nitric oxide (NO), total thiol (TT), and glutathione peroxidase (GPx) were measured in the prefrontal cortex. The protein levels of interleukin-1 beta (IL-1ß) and NLRP3-ASC-Caspase-1 axis were assessed by ELISA and Western blotting, respectively. Results showed that ZIN (100 mg/kg) had no antinociceptive activity, and subsequent experiments were performed at this dose. Repeated ZIN reversed MPH antinociceptive tolerance, whereas single ZIN did not. Single and repeated ZIN attenuated naloxone-induced jumping. In addition, repeated ZIN significantly inhibited weight loss. Repeated ZIN suppressed the MPH-induced increase in TBARS, NO, IL-1ß, NLRP3, ASC, and Caspase-1. It also inhibited MPH-induced TT and GPx reduction. In contrast, single ZIN had no effect. Findings suggest that ZIN reduces MPH-induced tolerance and dependence by suppressing oxidative stress and NLRP3 inflammasome activation. This study provides a novel therapeutic approach to reduce the side effects of MPH.

2-Hydroxybenzohydrazide as a novel potential candidate against nociception, inflammation, and pyrexia: in vitro, in vivo, and computational approaches.

The current study was designed to evaluate the 2-hydroxybenzohydrazide (HBH) as a drug having efficacy against pyrexia, inflammation, and nociception. Besides, the therapeutic effects of HBH on oxidative stress and C-reactive proteins were also evaluated. The pharmacological studies on HBH (20-60 mg/kg) were conducted using nociception, inflammation, and pyrexia standard models. Naloxone antagonism was performed to assess the possible involvement of opioidergic mechanisms. The antioxidant study was conducted on ABTS and DPPH assays using gallic acid as a standard. Moreover, the binding capability of HBH with enzymes cyclooxygenase-I/II (COX-I/II) was determined using molecular modeling analysis. The findings indicated that the HBH dose-dependently inhibited pain, inflammation, and pyrexia. The HBH has significant anti-nociceptive and anti-inflammatory activities at 60 mg/kg (***p < 0.001), similar to the lower doses of diclofenac sodium (50 mg/kg) and tramadol (30 mg/kg). The HBH at 60 mg/kg reduced pyrexia as paracetamol (150 mg/kg). The HBH at 20-60 mg/kg doses declined the plasma C-reactive protein concentration. The mechanistic studies showed that the anti-nociceptive effect of HBH was antagonized by naloxone, indicating that the opioidergic mechanisms are involved. Furthermore, computational studies showed that the HBH exhibited an affinity for COX-I/II target receptors. The HBH significantly inhibited ABTS and DPPH radicals (IC50 = 33.81 and 26.74 µg/ml). These results proposed that the HBH has significant antipyretic, anti-inflammatory, and anti-nociceptive activities involving opioidergic mechanism.

Adolescent morphine exposure changes the endogenous vlPAG opioid response to inflammatory pain in rats.

Adolescence is one of the most critical periods for brain development, and exposure to morphine during this period can have long-life effects on pain-related behaviors. The opioid system in the periaqueductal gray (PAG) is highly vulnerable to drug exposure. However, the impact of adolescent morphine exposure (AME) on the endogenous opioid system in the PAG is currently unknown. This study aims to investigate the long-lasting effects of AME on the endogenous opioid system and its involvement in altering nociceptive behaviors. Adolescent rats were given escalating doses of morphine (2.5-25 mg/kg, subcutaneous) or an equal volume of saline twice daily for 10 consecutive days (PND 31-40). After a 30-day washout period, adult rats underwent formalin tests following microinjection of morphine, naloxone, or saline into the ventrolateral PAG (vlPAG) region. The results indicated that morphine microinjection into the vlPAG of the adolescent morphine-treated group significantly reduced the nociceptive score. However, the analgesic response to morphine in this group was significantly lower compared to the saline-treated group during adolescence. Additionally, the nociceptive score significantly increased following naloxone but not saline microinjection into the vlPAG of the saline-treated group during adolescence, rather than the morphine-treated one. These findings indicate that AME has long-lasting effects on the endogenous opioid system in the vlPAG, which can consequently alter behaviors related to inflammatory pain in adulthood.

Antiseizure Effects of Peganum harmala L. and Lavandula angustifolia.

Peganum harmala L. and Lavandula angustifolia are two traditional herbs with probable antiseizure effects. This study evaluated the effects of these two herbal extracts on pentylenetetrazol- (PTZ-) induced seizures in mice. We prepared hydroalcoholic extracts using P. harmala seeds and the aerial parts of L. angustifolia and then randomly divided 190 mice into 19 groups. Normal saline (10 mg/kg), diazepam (2 mg/kg), P. harmala (2.5, 5, 10, 15, 30, 45, and 60 mg/kg), and L. angustifolia (200, 400, 600, and 800 mg/kg) were intraperitoneally (IP) administrated 30 min before an IP administration of PTZ (90 mg/kg). Animals were observed for behavioral changes for one hour. In addition, the effects of flumazenil and naloxone on the antiseizure activity of P. harmala and L. angustifolia were assessed. P. harmala showed antiseizure activity at the dose of 10 mg/kg; it prolonged the seizure latency and decreased the seizure duration. The mortality protection rate was 90% for this herbal extract. L. angustifolia (600 mg/kg) prolonged the seizure latency and decreased both seizure duration and mortality. Neither flumazenil nor naloxone significantly reversed the antiseizure activities of P. harmala and L. angustifolia. In mice, the hydroalcoholic extracts of P. harmala and L. angustifolia showed antiseizure activity against PTZ-induced seizures. We could not delineate the exact antiseizure mechanisms of these extracts in the current study.

Analgesic effect of the flavonoid herbacetin in nociception animal models.

OBJECTIVE: This study aimed to assess the antinociceptive activity of herbacetin using chemically and thermally induced nociception in a mouse model. MATERIALS AND METHODS: The antinociceptive effects of various herbacetin doses (50, 100, 150, and 200 µg/kg) were assessed in mice using the acetic acid-induced writhing test, hot plate test, and formalin-induced paw-licking assay. The effects were compared to those of mice treated with acetylsalicylic acid or morphine in the presence or absence of naloxone (an opioid receptor antagonist). Capsaicin- and glutamate-induced paw-licking tests were also used to evaluate the involvement of the vanilloid and glutamatergic systems, respectively. Pro-inflammatory mediators: Interleukin-1-beta (IL-1ß), Tumour Necrosis Factor alpha (TNF-α), Interferon-gamma (IFN-γ), and Nitric Oxide (NO) were also assessed. RESULTS: Herbacetin produced significant dose-dependent inhibition of nociceptive behavior in the acetic acid-induced writhing test, showing 65% inhibition at a dose of 200 µg/kg. Herbacetin also caused a significant increase in the latency period in response to the hot plate test (70% at 200 µg/kg), and significantly inhibited both the neurogenic and inflammatory phases in the formalin-induced paw-licking test. Naloxone significantly reverses the effect of herbacetin in both the hot plate and formalin-induced paw-licking test. Moreover, herbacetin significantly inhibited the neurogenic nociception induced by intraplantar injections of capsaicin and glutamate (75% and 48%, respectively, at a dose of 200 µg/kg). Pro-inflammatory cytokines IL-1ß, TNF-α, IFN-γ, and NO in the serum of mice were assessed. These cytokines were significantly inhibited by herbacetin (100 and 200  µg/kg). Thus, herbacetin exhibited peripheral and central antinociception through the modulation of vanilloid receptors, opioid receptors, and the glutamatergic system. CONCLUSIONS: Herbacetin possesses antinociceptive activity in adult mice that is mediated through both central and peripheral pathways.

Chronic Voluntary Morphine Intake Is Associated with Changes in Brain Structures Involved in Drug Dependence in a Rat Model of Polydrug Use.

Chronic opioid intake leads to several brain changes involved in the development of dependence, whereby an early hedonistic effect (liking) extends to the need to self-administer the drug (wanting), the latter being mostly a prefrontal-striatal function. The development of animal models for voluntary oral opioid intake represents an important tool for identifying the cellular and molecular alterations induced by chronic opioid use. Studies mainly in humans have shown that polydrug use and drug dependence are shared across various substances. We hypothesize that an animal bred for its alcohol preference would develop opioid dependence and further that this would be associated with the overt cortical abnormalities clinically described for opioid addicts. We show that Wistar-derived outbred UChB rats selected for their high alcohol preference additionally develop: (i) a preference for oral ingestion of morphine over water, resulting in morphine intake of 15 mg/kg/day; (ii) marked opioid dependence, as evidenced by the generation of strong withdrawal signs upon naloxone administration; (iii) prefrontal cortex alterations known to be associated with the loss of control over drug intake, namely, demyelination, axonal degeneration, and a reduction in glutamate transporter GLT-1 levels; and (iv) glial striatal neuroinflammation and brain oxidative stress, as previously reported for chronic alcohol and chronic nicotine use. These findings underline the relevance of polydrug animal models and their potential in the study of the wide spectrum of brain alterations induced by chronic morphine intake. This study should be valuable for future evaluations of therapeutic approaches for this devastating condition.

On-Demand Opioid Effect Reversal with an Injectable Light-Triggered Polymer-Naloxone Conjugate.

Misuse of opioids can lead to a potential lethal overdose. Timely administration of naloxone is critical for survival. Here, we designed a polymer-naloxone conjugate that can provide on-demand phototriggered opioid reversal. Naloxone was attached to the polymer poly(lactic-co-glycolic acid) via a photocleavable coumarin linkage and formulated as injectable nanoparticles. In the absence of irradiation, the formulation did not release naloxone. Upon irradiation with blue (400 nm) light, the nanoparticles released free naloxone, reversing the effect of morphine in mice. Such triggered events could be performed days and weeks after the initial administration of the nanoparticles and could be performed repeatedly.